The invention relates to a centrifugal pump assembly with an electric drive motor and with a control device having a frequency converter, for controlling the rotational speed of the drive motor.
Centrifugal pump assemblies are known, with which the electrical drive motor is activated by way of a frequency converter, in order to be able to vary the rotational speed of the drive motor and thus of the centrifugal pump assembly. Thereby, it is very desirable to be able to operate the pump assembly with the greatest possible efficiency. The maximum hydraulic power which is available, with known centrifugal pump assemblies, is limited by the maximum frequency as well as the maximum load cycle of the frequency converter. Thereby, the pump assemblies as a rule are designed in a manner such that at least one point of the pump characteristic line with a maximum rotational speed, the maximum load cycle is given by maximum output voltage of the frequency converter, so that the maximum electrical power of the pump is reached there. This however leads to the fact that in other regions of the pump characteristic line with maximum rotational speed, the maximum electrical power of the drive motor which is available is not utilized. This means that there are regions in which the maximum electrical power which is available may not be completely converted into hydraulic power of the pump assembly. In these regions, it is not possible to further increase the pump rotational speed by way of the usual control of the frequency converter, since already the maximum voltage and/or the maximum load cycle of the frequency converter are reached. This means that with a conventional pump control, the maximum electrical power may not be utilized over the whole operating range of the pump.